This application claims the priority of German patent application number 10 2007 038 634.8, filed Aug. 16, 2007, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an impulse-absorbing structural component for an aircraft.
German patent document DE 101 29 576 A1 discloses a structural element with an energy-absorbing layer inserted between two covering layers, in which at least one covering layer is load-bearing. The planar energy-absorbing layer is connected to the covering layers only at the edges, and has a higher elongation in case of a break than the covering layers. This arrangement has the disadvantage that, although it can absorb impulses, it has either an increased weight with the same strength, or a reduced strength with the same weight. Because the energy-absorbing layer is accommodated between the covering layers, the latter experience a notch effect, particularly under a load. The energy-absorbing layer which is used is dry or low-resin aramid woven fabric or PBO, which is connected to a load-bearing shell. This means that tensile forces cannot be transmitted transversely to the plane of the component, so that it is at risk under certain operating loads. Moreover, the two covering layers may also arch apart in response to compressive forces which may occur in the plane of the covering shells.
German patent document DE 10 2004 029 485 B1 discloses an impulse-absorbing structural component for an aircraft with two covering layers and an intermediate layer disposed therebetween. The material of the intermediate layer is selected so that it has a greater elongation at break than do the two covering layers. The intermediate layer extends in an alternating manner between the covering layers such that, should a mass impact on it, an intercept bag forms which dissipates the kinetic energy of the mass. This component, however, has the disadvantage that it is very expensive to manufacture. Moreover, tests have shown that the functional performance of the intercept bag is in some cases limited, as tears can occur in the intercept bag in a particular case.
One object of the present invention is therefore to provide an impulse-absorbing structural component which can be produced with a low manufacturing expenditure, and which assures a high degree of reliability.
This and other objects and advantages are achieved by the impulse absorbing structure component according to the invention, which comprises a three-dimensional impulse-absorbing layer having a regular pattern of elevations and depressions. A covering layer is applied to the elevations of the impulse-absorbing layer, while the other areas of the impulse-absorbing layer are raised from the covering layer. The material of the impulse-absorbing layer has a greater stretching or elongation at its breaking point than does the covering layer. Should a mass impact on the covering layer, an intercept bag which forms in the impulse-absorbing layer dissipates the kinetic energy of the mass.
Viewed in the direction of the spread of the intercept bag, the structural component according to the invention has an open structure after the impulse-absorbing layer, such that the formation of the intercept bag can take place without interaction with elements of the structural component. It is therefore impossible for the intercept bag to be damaged, so that its functional performance is not limited.
The covering layer serves in particular to absorb and transmit the operating loads and to guarantee the dimensional stability of the component, and therefore is of a higher strength than the impulse-absorbing layer. However, the impulse-absorbing layer also contributes significantly through its design to the stiffness of the component.
The thickness of the covering layer can in particular be between 3 and 5 mm in order to make the structure sufficiently strong. Advantageously, it is made of a high strength carbon-fiber-reinforced plastics material (CFK). The fibrous material can in this respect be both unidirectional or in the form of woven fabric or knitted fabric.
The impulse-absorbing layer advantageously consists of a glass-fibre-reinforced plastics material (GFK) of a high elongation at break. In this case the fibrous material is advantageously in the form of woven fabric or knitted fabric. The thickness of the impulse-absorbing layer is preferably in the range of 0.5-1 mm.
Epoxy resins and thermoplastics in particular are suitable as matrix materials for the above-mentioned layers as well as for all the other fiber-reinforced layers which are described in this patent application.
In a particularly advantageous embodiment, a further layer of the same form is applied to the impulse-absorbing layer. In other words: this results in a three-dimensional total layer which comprises elevations and depressions and consists of two sub-layers, namely the impulse-absorbing layer and the further layer, the further layer having a lower elongation at break than the impulse-absorbing layer. The further layer is in this case disposed between the covering layer and the impulse-absorbing layer. It serves in particular to increase the stiffness of the component and can correspond to the covering layer with regard to the materials used and their elongation at break.
In this respect the further layer is preferably of a layer thickness of 0.5-1.5 mm. It consists in particular of a carbon-fiber-reinforced plastics material (CFK) of high strength. Here the fibrous material can be both unidirectional or multidirectional and is in the form of woven fabric or knitted fabric.
In a configuration of this kind the impulse-absorbing layer can have the same properties as in the case of the construction described above without a further layer. That is, it is in particular of a thickness of 0.5-1.0 mm and advantageously consists of a glass-fiber-reinforced plastics material (GFK) of a high elongation at break, with the fibrous material being in particular in the form of woven fabric or knitted fabric.
The impulse-absorbing layer and optionally the further layer disposed thereon may be of wavy formation, in which case, in addition to a rounded form (e.g. semicircular, sinusoidal), the individual wave crests and wave troughs can also be of triangular or trapezoidal formation.
In further constructions the impulse-absorbing layer is of knob-shaped or eggbox-shaped formation.
The structural component according to the invention prevents damage to functionally essential components of aircraft, land vehicles or watercraft or tools, machines, systems and building parts as a result of the transmission of impulses through the impact of birds, hydrodynamic pressure surges or pressure waves—in particular through explosions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.